Maintenance of a viable airway is critical to patient safety during surgical procedures conducted under general anaesthetic. Maintenance of a viable airway during such surgical procedures had, for many years, been achieved by insertion of an endo-tracheal tube into the patient. The endo-tracheal tube was typically inserted through the oral cavity or nasal cavity, into the larynx, through the vocal cords and into the trachea. As the endo-tracheal tube had to be inserted through the vocal cords, difficulty was often experienced in correctly positioning the endo-tracheal tube.
British patent no. 2,111,394 (which corresponds to U.S. Pat. No. 4,509,514) describes a device for maintaining an airway in a patient. The device is described as being an artificial airway device. The device comprises a curved, flexible tube opening at one end into the interior of a hollow mask portion shaped to conform to fit readily into the actual and potential space behind the larynx and to seal around the circumference of the laryngeal inlet without penetrating into the interior of the larynx. Commercial forms of this device have an inflatable collar extending around the periphery of the mask. The inflatable collar is adapted to form the seal around the laryngeal inlet when the collar is inflated. Additionally, the mask portion included an inflatable posterior part which is adapted to press against the back of the throat and thereby increase the sealing pressure around the laryngeal inlet.
British patent no. 2,111,394 states that the shape and (when fitted) the inflatable part or parts of the mask ensure that it approximates closely to the shape of the space between the laryngeal inlet and the walls of the lower part of the throat behind it. Since the walls of tissue forming the back of the throat are relatively rigid, inflation of the mask forces it more tightly against the tissues surrounding the laryngeal inlet, so forming an airtight seal, while tending to anchor the mask in position.
In use of the device described in GB 2,111,394, the device is inserted through the mouth of the patient and down the throat past the epiglottis until the mask comes to rest with its distal end in the base of the throat, lying against the upper end of the normally closed oesophagus. The inflatable ring on the mask is then inflated to seal around the inlet to the larynx. The patient's airway is thus secure and unobstructed and the laryngeal mask can be connected directly to conventional anaesthetic circuit hosing for either positive pressure or spontaneous breathing.
In the device of GB 2,111,394, the mask is associated with an air tube through which air may be passed in order to inflate the inflatable ring, meaning that the device of GB 2,111,394 (the mask and associated air tube) is essentially linear in construction. However, when the device is inserted into a patient, it must follow a curved path as it passes through a patient's mouth and into the throat.
This means that, in order to insert the mask into a patient, a user must manually bend the device to guide it around the curved path into the patient's throat. However, the user must avoid putting his or her fingers into the patient's mouth when inserting the device, meaning that the manual bend placed in the device by the user must be released when the user's fingers come into contact with the patient's teeth. In many cases, such as in cases of patients having long necks, a user will be forced to release the manual bend in the device prior to the device being positioned correctly within the patient's throat. Thus, correctly locating the device in the patient's throat is often difficult and requires additional manipulation.
Some attempts have been made to overcome this problem. For instance, a curved metal introducer may be used in conjunction with the device of GB 2,111,394 that acts in a similar manner to a shoehorn to guide the device into place in the patient's throat. However, both inserting and removing a metal introducer from a patient's throat can be difficult. In addition, inserting a metal device into a patient's mouth and throat has the potential to cause the patient discomfort or injury if the procedure is not carried out correctly.
Other attempts to overcome this problem have included fabricating laryngeal masks having a permanent curve out of rigid or semi-rigid materials. However, the drawback of these devices is that, due to their shape and the material from which they are fabricated, the tip of the device must contact the back of a patient's throat during insertion so that the device may be guided into position. This contact between the device and the patient's throat has the potential to lead to injury to, or discomfort for, the patient.
Thus, there would be an advantage if it were possible to provide a laryngeal mask that was simple and straightforward to correctly insert that minimised the risk of injury or discomfort to the patient.
It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.
Throughout this specification, the term “comprising” and its grammatical equivalents shall be taken to have an inclusive meaning unless the context of use indicates otherwise.